Silicon carbide (SiC) is a semiconductor that has a wider bandgap than that of silicon (Si). Accordingly, SiC has a higher breakdown voltage and a higher melting point compared to Si. In view of these beneficial properties, SiC is a semiconductor material that is expected to be applied to next-generation power electronic devices, RF devices, high-temperature-operating devices and so on. It is also known that SiC can take various crystal structures including cubic ones such as 3C—SiC and hexagonal ones like 6H—SiC and 4H—SiC.
FIG. 12 is a cross-sectional view schematically showing the structure of a known NMOS (Metal Oxide Semiconductor)-FET (Field Effect Transistor) that uses SiC. FIG. 12 shows p-type doped channel SiC layer 102 that has been grown epitaxially on the surface of a p-type SiC substrate 101 doped with aluminum (a p-type impurity) at a concentration of 1×1018 atoms·cm−3; n-type source/drain regions 103a and 103b doped with nitrogen (an n-type impurity) at a concentration of 1×1018 cm−3 and formed in the doped channel SiC layer 102; gate insulating film 104 of SiO2 formed on the doped channel SiC layer 102; gate electrode 105 made of an Ni alloy film and formed on the gate insulating film 104; source/drain electrodes 106a and 106b made of an Ni alloy film in ohmic contact with the respective source/drain regions 103a and 103b; and backside electrode 107 made of an Ni alloy film in ohmic contact with the back surface of the SiC substrate 101.
In this structure, if a constant voltage is applied between the source/drain electrodes 106a and 106b, and another voltage (a gate voltage) is applied to the gate electrode 105, a current flowing between the source/drain regions 103a and 103b is modulated in accordance with the gate voltage so that a switching operation is performed. In particular, a MOSFET formed on a SiC substrate has higher breakdown voltage characteristic than those of a MOSFET formed on a Si substrate, and is highly regarded as a power electronic device that can supply a large current as well as expected to be implemented as an RF device.